Adaptive sliding mode control for dual-arm space robots post-capturing spinning targets

Non-cooperative objects in space, such as defunct spinning satellites and tumbling space debris, pose significant risks to future space missions. To mitigate these risks, autonomous strategies for capturing non-cooperative targets are required. Autonomous free-floating space robots (FFSRs) are proposed as a solution for in-orbit capture operations, which typically involve four phases: observation, approach, capture, and post-capture stabilization. Dual-arm FFSRs offer advantages over single-arm FFSRs by enabling more effective manipulation through the cooperative use of both arms. This study presents an adaptive sliding mode control (ASMC) approach for dual-arm FFSRs with strong robustness against model uncertainties in target inertial parameters, enabling precise coordinated control of both the base attitude and the manipulators, when the coupled dynamics between the base and the dual manipulators exist. Smooth motion for the dual end-effectors is planned using Bezier curves, ensuring safe trajectories for stabilizing the spinning target. Compared to traditional sliding mode control (SMC), which is known for its robustness against uncertainties, ASMC eliminates the chattering effects of SMC that cause vibrations in the manipulators. Although high-order SMC also can remove chattering, it requires high computational complexity due to the need for real-time estimation of higher-order derivatives. The stability of the proposed ASMC is thoroughly proven using the Lyapunov method, demonstrating that ASMC effectively controls dual-arm FFSRs and reduces computational complexity by adjusting adaptive control gains to smooth frequent switches causing the chattering effects. Numerical simulations validate the proposed ASMC, showing higher control accuracy and stronger robustness against model uncertainties than SMC, with successful deceleration and stabilization of the spinning target and base attitude in the post-capture task.